The manufacture and use of semiconductor devices as non-volatile memory devices (e.g., memory devices capable of retaining data even after power to the device has been turned off) have increased dramatically in response to recent developments in the technology. Flash memory is an increasingly popular type of non-volatile memory. Each memory cell of a flash memory device is typically created as a transistor provided with a floating gate or an insulating film as a so-called charge storage layer. Data is recorded by storing electric charges in a charge accumulation layer. A conventional implementation of Flash memory includes a Silicon Oxide Nitride Oxide Silicon (“SONOS”) structure for storing the electric charge in a trap layer in the Oxide film/Nitride film/Oxide film (“ONO” film) and having an insulating film as the charge storage layer.
International Application Published under the Patent Cooperation Treaty No. 2007-013155 discloses a semiconductor device having a bit line formed in the semiconductor substrate using the diffusion region, and a plurality of word lines which intersect with the bit line formed on the semiconductor substrate. In the aforementioned semiconductor device, the bit line formed in the diffusion region exhibits a high resistance. Bit line contact regions are formed at each section the bit line reaches after passing across a plurality of word lines (for example, 16 lines) for the purpose of electrically coupling between the bit line and a metal interconnection layer.
However, according to the aforementioned International Application, the proximity effect resulting from exposure of the photoresist for forming the word line increases the width of the word line adjacent to the bit line contact region to be larger than that of the other word lines. The International Application discloses a technology for providing a “dummy layer” in the bit line contact region upon formation of the word line so that the proximity effect is suppressed. However, the width of the dummy layer is larger than that of the word line, and thus fails to sufficiently suppress the proximity effect. As a result, the width of the word line adjacent to the bit line contact region becomes different from that of the other word lines. The width of a word line corresponds to the gate length of the transistor which forms the memory cell. As such, the transistor adjacent to the bit line contact region may have different properties from that of other transistors in the flash memory.